Notes: Explanations for the terms Structurally Deficient and
Functionally Obsolete can be found on pages 14 and 15 in Chapter 3 of the
Federal Highway Administration, 2006 Conditions and
Performance Report, available at
http://www.fhwa.dot.gov/policy/2006cpr/pdfs/chap3.pdf as of September 2009.U.S. totals include the 50 states, the District of Columbia, and
Puerto Rico. Data include: Rural-Interstate, principal arterial, minor
arterial, major collector, minor collector and local roads; urban-interstate,
other freeways or expressways, other principal arterial, minor arterial,
collector, and local roads. Data for 1990, 2007 and 2008 are as of December of those years
and for 2000 as of August of that year.

Sources: Federal
Highway Administration, Office of Bridge Technology, National Bridge
Inventory Database, Count, Area, Length of
Bridges by Highway System, available at
http://www.fhwa.dot.gov/bridge/britab.htm as of March 2009 as reported in
U.S. Department of Transportation, Research and Innovative Technology
Administration, Bureau of Transportation Statistics, National Transportation Statistics, Table 1-27, available at http://www.bts.gov as of
September 2009.